During 1996, approximately 236,000 persons received hemodialysis in the United States; of these, an estimated 183,000 (78%) received chronic hemodialysis. Patients who receive chronic hemodialysis are at increased risk for bloodstream infections (BSIs) because of the need for repeated vascular access. Reported BSI rates for hemodialysis patients have ranged from 8.4 to 16.8 episodes per 100 patient-years, and BSI has been identified as the cause of death in 6%-18% of hemodialysis patients. Outbreaks of BSIs in hemodialysis units usually have been caused by inadequate disinfection of 1) water treatment or distribution systems and 2) reprocessed dialyzers. This report summarizes the investigations of three clusters of gram-negative bacterial BSIs at hemodialysis centers in Canada, the United States, and Israel. The findings indicate that all three outbreaks probably resulted from contamination of the waste drain ports in the same model of hemodialysis machine.